1. Field of Invention
The present invention provides liquid-solid separators, particularly portable separators for treatment of sludge in bulk. More specifically, the present invention provides an improved filtration system for extracting liquid from a sludge or slurry and separating the resulting liquids and solids for separate disposal or recovery.
2. Description of the Prior Art
Liquid-solid separators have been used to remove the liquid from solids in a sludge. The term sludge is widely used to refer to a variety of mixtures and generally includes any solid-liquid mixture or slurry such as sewage and industrial waste. The sludge contains any ratio of liquids to solids. The sludge often has had substantially more liquid material than solid material. Separation of the sludge into its liquid and solid components, also known as xe2x80x9cdewatering,xe2x80x9d has been desirable for recovery or disposal of the one or both of the components.
Liquid-solid separators have been desirable for several reasons. Environmental regulations have required the water content of solid waste to be below specified levels before it is accepted in a landfill. Solid waste frequently had to be hauled to a disposal site; freight carriers, as well as the disposal site operation, often charged based on the weight. Also, in many industrial processes, the finished product would be either a solid or a liquid contained in a sludge, and it has been necessary to separate the solid from the liquid phase in order to isolate the finished product.
Generally, during separation, the fluid component of the sludge has been drawn through a filter in one of two ways, vacuum drainage or gravitational drainage. Vacuum drainage required the use of a pump in flow communication with the filtrate cavity of the filter. In order to utilize a pump that can develop a vacuum, the filtrate cavity had to remain below the liquid surface level at all times. In this type of system, activation of the pump drew the sludge liquid as well as the sludge solids toward the filters thus often resulted in filter blockage. During the initial stages of dewatering, when the liquid concentration was highest, the smaller sludge solid particles more readily flowed toward the filter and tended to block the filter element. Blockage of the filter element hindered dewatering speed and efficiency.
The other typical manner of dewatering sludge was gravitational drainage which involved placing the sludge into a container that had filters therein. The liquid in the sludge passed through the filters and thence from the container; however, the filters did not permit the solids to pass through. Therefore, the solids remained in the container and were removed after the dewatering operation had been completed.
Gravitational drainage did not require a vacuum, therefore, did not require the maintenance of the filtrate cavity below the sludge liquid surface. Consequently, the filters in such a system extended the entire height of the container and, thereby, provided greater drainage surface area. In gravitational drainage the sludge solid particles settled on the filter surface in a more uniform manner and provided an additional filtering layer. Thus, the filters did not experience blockage; however, gravitational drainage was slow.
One type of prior art separator is disclosed in U.S. Pat. No. 6,004,461. A phase separator had a tank having a bed and surrounding sides. A metal support plate grating is supported by the bed and walls in a manner that left a space between the grating and the wall and the bed to have a liquid collection space that collects the filtered liquid. A screen was attached to the grating which was used to distribute the weight of the sludge on the grating so that the filter did not sag down into the spaces in the grating and become lodged or torn. A filter positioned over the screen and grating, and sludge was placed in the tank on top of the filter. The liquid in the sludge moved through the filter, screen, and grating into the liquid collection space. Movement of the sludge through the filter, screen, and grating was accomplished by gravity, hydrostatic pressure, and by wicking or capillary action. The completed dewatering of the sludge, so far as is known, required approximately six days. A drain was provided to allow such liquid to be released from the tank. The dewatered sludge along with the filter and screen was disposed at the disposal site.
Filter boxes have used superimposed metal support plate and screens in order to prevent the filter from extending into the metal support plates and tearing the filter. The forces exerted on the filter by the large amounts of sludge introduced into the filter box required metal support plates commonly having less than forty (40) percent pore space. These metal support plates were used due to their strength which permitted them to withstand the force of the incoming sludge. One common type of support plate was known in the industry as xe2x80x9cperforated plate.xe2x80x9d The filter media support structure was formed of perforated metal plates having approximately forty (40) percent pore space. Additionally, a screen was placed on the perforated metal plates in order to prevent sagging and tearing of the filter. The perforated metal plate and screen were the primary element that contributes to the length of time required to filter sludge in a gravitational drainage dewatering system. The perforated plates provided strong support for the filter but with decreased pore space. This was a primary reason the gravitational sludge dewatering systems required a longer amount of time to dewater the sludge.
The present invention provides a liquid-solid separator with a tank having side walls and a floor. The inside of the tank supports a filter media support structure. The filter media support structure is primarily formed of expanded metal. With the present invention, it has been found that expanded metal filter media support structure containing at least eighty-six (86) percent pore space can be used. The use of the expanded metal filter media support structure significantly reduces filtration time for a given volume of sludge, thus, permitting the filtering of the sludge at a rate significantly faster than the prior art. Further, with the present invention, it has been found that only certain locations in the separator tank need be reinforced against the weight and load of the solids in the incoming sludge. These have been found to be the first fifteen to thirty percent of the linear extent of the filter media support structure extending away from the sludge inlet ports of tank. A preferred portion of such linear extent has been found to be about twenty percent, although other variations may be used. In those areas where reinforcement against sludge weight is necessary, perforated plate filter media support structure are used.
Filter media support structure surfaces overlaying the exterior walls, the bed, and the dividing wall are covered by a high tensile strength monofilament polyester fiber filter media which serves as a liquid permeable filter screen. Additionally, it has been found that the high tensile strength monofilament polyester fiber filters can be used to facilitate filtering; to increase the longevity of the separator; and to be reused continually for approximately five years.
Gravity and hydrostatic pressure force the liquid from the sludge through the filter and into the space between the walls of the separator and the filter media support structure. The exit ports located in the bed of the tank permits the liquid to be removed.
When the sludge dries, the tank is loaded as a unit onto a transport truck or trailer and transported to a desired location, such as a landfill or other solid waste disposal site. There, the solids can be removed, leaving the tank and the high tensile strength monofilament polyester fiber filter media ready to be used again.
In its preferred form, the tank has a dividing wall is placed in the center of the tank along the longitudinal axis of the tank and perpendicular to the tank bed. The dividing wall allows liquid in the center of the tank to drain more thoroughly and more quickly by providing increased drainage surface area and decreasing the distance fluid must travel. Additionally, the outer walls contain a hinged door; sludge inlet ports, to permit the sludge to enter the tank from a storage or mixing tank; and exit ports, which are used to drain the filtered liquid out of the tank.